A renewable energy source as well as a solar cell does not use fossil fuels which are limited to exist in the Earth, and they have attracted attention as an alternative energy of today in that they minimize environmental pollution. However, since voltage and current of the renewable energy source are unstable, it is not easy to stably supply power to a load. Therefore, a technology that stabilizes the power outputted from a system is being developed by using an energy storage device such as a battery.
A renewable power generation system in the related art has a structure that supplies a required power to a load by sequentially connecting a plurality of power converters from a plurality of power sources. Due to a capacity difference between respective cells between stacks of solar cell modules that correspond to battery stacks (a pack of cells connected in series) inserted in the respective connected portions thereof or a battery (a chemical battery), deviation of charging amount of the batteries may occur. In order to prevent the deviation of the charging amount between the batteries, a charging balance circuit (balancing circuit) is used separately from the power converter.
FIG. 1 illustrates a cell balancing circuit of the related art. Diagram (a) of FIG. 1 is a schematic circuit for charging, and diagram (b) of FIG. 1 is a schematic circuit for discharging. In the related art, the cell balancing circuit having the configuration as shown in FIG. 1 and a charging/discharge circuit for ripple removing (circuit for removing ripples occurring due to alternating current (AC) at a direct current (DC) terminal) are present separately, thus costs and volume of the product may increase, and efficiency and reliability thereof may deteriorate.
Further, in the related art, a high capacity electrolytic capacitor is used for removing ripples of direct current voltage at a DC link. However, the electrolytic capacitor is high-capacity, while its life is short.
The background art of the present invention is disclosed in the Korean Patent Laid-Open Publication No. 2011-0132977 (laid-open on Dec. 9, 2011).
The above information disclosed in this Background section is only to enhance the understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.